linux-kernel - [PATCH 2/4] sched_ext: Add scx_bpf_task_set_slice() and scx_bpf_task_set_dsq

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Message-ID: <20251007015147.2496026-3-tj@kernel.org>
Date: Mon,  6 Oct 2025 15:51:45 -1000
From: Tejun Heo <tj@...nel.org>
To: David Vernet <void@...ifault.com>,
	Andrea Righi <arighi@...dia.com>,
	Changwoo Min <changwoo@...lia.com>
Cc: linux-kernel@...r.kernel.org,
	sched-ext@...ts.linux.dev,
	Tejun Heo <tj@...nel.org>
Subject: [PATCH 2/4] sched_ext: Add scx_bpf_task_set_slice() and scx_bpf_task_set_dsq_vtime()

With the planned hierarchical scheduler support, sub-schedulers will need to
be verified for authority before being allowed to modify task->scx.slice and
task->scx.dsq_vtime. Add scx_bpf_task_set_slice() and
scx_bpf_task_set_dsq_vtime() which will perform the necessary permission
checks.

Root schedulers can still directly write to these fields, so this doesn't
affect existing schedulers.

Signed-off-by: Tejun Heo <tj@...nel.org>
---
 kernel/sched/ext.c                       | 30 ++++++++++++++++++++++++
 tools/sched_ext/include/scx/common.bpf.h |  2 ++
 2 files changed, 32 insertions(+)

diff --git a/kernel/sched/ext.c b/kernel/sched/ext.c
index fc353b8d69f7..6d76efaaa9b2 100644
--- a/kernel/sched/ext.c
+++ b/kernel/sched/ext.c
@@ -5833,6 +5833,34 @@ static const struct btf_kfunc_id_set scx_kfunc_set_unlocked = {
 
 __bpf_kfunc_start_defs();
 
+/**
+ * scx_bpf_task_set_slice - Set task's time slice
+ * @p: task of interest
+ * @slice: time slice to set in nsecs
+ *
+ * Set @p's time slice to @slice. Returns %true on success, %false if the
+ * calling scheduler doesn't have authority over @p.
+ */
+__bpf_kfunc bool scx_bpf_task_set_slice(struct task_struct *p, u64 slice)
+{
+	p->scx.slice = slice;
+	return true;
+}
+
+/**
+ * scx_bpf_task_set_dsq_vtime - Set task's virtual time for DSQ ordering
+ * @p: task of interest
+ * @vtime: virtual time to set
+ *
+ * Set @p's virtual time to @vtime. Returns %true on success, %false if the
+ * calling scheduler doesn't have authority over @p.
+ */
+__bpf_kfunc bool scx_bpf_task_set_dsq_vtime(struct task_struct *p, u64 vtime)
+{
+	p->scx.dsq_vtime = vtime;
+	return true;
+}
+
 static void scx_kick_cpu(struct scx_sched *sch, s32 cpu, u64 flags)
 {
 	struct rq *this_rq;
@@ -6638,6 +6666,8 @@ __bpf_kfunc void scx_bpf_events(struct scx_event_stats *events,
 __bpf_kfunc_end_defs();
 
 BTF_KFUNCS_START(scx_kfunc_ids_any)
+BTF_ID_FLAGS(func, scx_bpf_task_set_slice, KF_RCU);
+BTF_ID_FLAGS(func, scx_bpf_task_set_dsq_vtime, KF_RCU);
 BTF_ID_FLAGS(func, scx_bpf_kick_cpu)
 BTF_ID_FLAGS(func, scx_bpf_dsq_nr_queued)
 BTF_ID_FLAGS(func, scx_bpf_destroy_dsq)
diff --git a/tools/sched_ext/include/scx/common.bpf.h b/tools/sched_ext/include/scx/common.bpf.h
index 06e2551033cb..505231b7b7ae 100644
--- a/tools/sched_ext/include/scx/common.bpf.h
+++ b/tools/sched_ext/include/scx/common.bpf.h
@@ -102,6 +102,8 @@ s32 scx_bpf_pick_any_cpu_node(const cpumask_t *cpus_allowed, int node, u64 flags
 s32 scx_bpf_pick_any_cpu(const cpumask_t *cpus_allowed, u64 flags) __ksym;
 bool scx_bpf_task_running(const struct task_struct *p) __ksym;
 s32 scx_bpf_task_cpu(const struct task_struct *p) __ksym;
+bool scx_bpf_task_set_slice(struct task_struct *p, u64 slice) __ksym __weak;
+bool scx_bpf_task_set_dsq_vtime(struct task_struct *p, u64 vtime) __ksym __weak;
 struct rq *scx_bpf_cpu_rq(s32 cpu) __ksym;
 struct rq *scx_bpf_locked_rq(void) __ksym;
 struct task_struct *scx_bpf_cpu_curr(s32 cpu) __ksym __weak;
-- 
2.51.0